i have an error to display alert message and does not validate the condition what is the solution

/**

*@NApiVersion 2.0

*@NScriptType ClientScript

*/

define(['N/record', 'N/ui/dialog'], function (record, dialog) {

    function validateField(context) {

        var currentRecord = context.currentRecord;

        if (context.fieldId == 'custrecordphoneno') {

            var phoneno = currentRecord.getValue({

                fieldId: 'custrecordphoneno'

            });

            if (phoneno.length >= 12 ){

       

                alert("please enter below  12 digits in the phoneno field");

               

            }

            var regex =/^[0-9]+$/; // Regular expression to allow only numbers

            if (!regex.test(phoneno)) {

                alert("Please enter only numbers (0-9) in the phone number field");

                return false;

            }

        }

        return true;

    }

 

    function onChange(context) {

        var currentRecord = context.currentRecord;

        var newValue = currentRecord.getValue('custrecordphoneno');

        var regex = /^[0-9]+$/;

 

        if (newValue) {

            if (!regex.test(newValue)) {

                alert('Please enter only numbers (0-9) in the phone number field');